An air compressor is widely being used in a construction site to supply compressed air to a driving tool, such as a nail driving machine, using compressed air. The air compressor generates compressed air in a compressed air generating unit by driving a motor unit, and stores the generated compressed air in a tank unit. The stored compressed air of high pressure is reduced to predetermined pressure by a pressure reducing valve and then is supplied to the driving tool (for example, see Patent Document 1).
A user may set the pressure of the air compressor to a state suitable for a work condition, by setting the use mode of the air compressor depending on the use condition of the driving tool or the like. For example, the air compressor has four use modes, that is, a low pressure mode, a normal pressure mode, a high pressure mode, and a ultra-high pressure mode, depending on a pressure state in the tank unit. Further, since there is a combination of three modes, namely, a normal operation mode, a power mode (quick charge mode), and a silent mode for each use mode, it is possible to set a mode of a plurality of patterns in total.
Patent Document 1: Japanese Patent Publication No. 2009-55719
However, it is not easy for a user to properly determine and select the mode setting of the plurality of patterns, depending on an operating condition. Further, an operation of changing the mode setting of the air compressor depending on the work condition causes inconvenience to many users. Hence, in order to supply a sufficient amount of compressed air to the driving tool under any work condition, the use mode is often set to a higher mode, such as the high pressure mode or the ultra-high pressure mode that keeps the pressure in the tank unit high.
As such, when the use mode of the air compressor is set to the higher mode, the pressure in the tank unit is set to a high value. The higher the pressure is, the less compression efficiency is. Thus, until the air compressor starts and then the pressure value in the tank unit reaches a motor stop pressure value, a relatively long time may be required, a driving sound caused by the driving of the motor unit may be generated for a relatively long time, and driving power may be increased. Further, since the pressure in the tank unit is kept high, high pressure load may be applied to the motor unit, the tank unit, the compressor (compressed air generating unit) and the like, and components may be worn out. Consequently, this leads to a reduction in durability.
Meanwhile, when the use mode of the air compressor is set to a lower mode such as the low pressure mode or the normal pressure mode, when pressure in the tank unit is lowered by using the driving tool, the compressed air for adequately driving the driving tool becomes rapidly insufficient, and work using the driving tool should be ceased until the pressure in the tank unit rises.